Nice theory, assumes that prices stay below your threshold long enough for the car to charge. It can happen, as your examples show, but can it happen at scale, i.e. when 1 in 10 people are running "full house equivalent" energy requests every time the price drops below say 0.02 EUR/kWh?

Been pricing electicity derivatives at work last week; with that context I'm now thinking of your scheme as a limit order, and what happens when the market is oversaturated with limit order?